On your iOS device, go to Settings > General > Software Update. If a newer version of iOS is available, follow the onscreen instructions to download and install it.
Make sure you have a recent backup to restore from.
On your iOS 8 device: Go to Settings > iCloud > Storage > Manage Storage, then tap a device listed under Backups to see the date and size of its latest backup.
On your iOS 7 device: Go to Settings > iCloud > Storage & Backup > Manage Storage, then tap a device listed under Backups to see the date and size of its latest backup.
For information about backing up manually now, see Back up your iOS device to iCloud. If you don’t see a backup you expected to be there, see the Apple Support article If you need help restoring from an iCloud backup.
Go to Settings > General > Reset, then tap “Erase all content and settings.”
In the Setup Assistant, proceed to “Set up your device,” tap Restore from a Backup, then sign in to iCloud.
Proceed to “Choose backup,” then choose from a list of available backups in iCloud.
For help deciding which backup to restore from, including information about restoring from another device’s backup, see the Apple Support article If you need help restoring from an iCloud backup.
However, this will delete all the data on the iPod and put the iPhone data in. Ignore the iOS 7 and iOS 8. They are there for distinguishment.
Best Answer
Can you try disabling iCloud syncing for the said app, if it doesn't trouble you much ?
iBooks for iPhone showed the same behaviour, automatically deleting books despite available storage. I had to turn off iCloud for iBooks .